This invention relates to valve stem seals utilized in intake and exhaust manifolds of internal combustion engines. More particularly, this invention relates to sealing elements in valve stem seals which assure against oil leakage at the tops of valve guides.
Internal combustion engines contain intake and exhaust valves, each valve including a head and a stem integrally fixed to the head, and reciprocally mounted in a guide. As the valve stem ordinarily operates in a substantial volume of oil, much effort is directed to limiting the amount of oil consumed by the engine. In order to control oil consumption, valve seals are mounted on valve guides to meter oil flow between the stems and guides.
A significant number of valve stem seal assemblies include a metallic casing or shell adapted to retain a resilient seal member, typically made of an elastomer or a polytetrafluoroethylene base material. Much effort has been directed to the shape of the resilient portion of the seal, particularly to the extent that the seal must not only engage the stem, but must also directly engage a portion of the valve guide itself.
A major problem in designing seals relates to tolerance variations encountered in the manufacture of seal assembly parts. Tolerance variations in the valve assembly casings designed for securement to valve guides affect those portions of the seal which engage the valve guide and valve stem. Thus, inadequate sealing caused by tolerance variations may result in excessive oil consumption, notwithstanding the purpose of the seal. Several designs have been offered to compensate for tolerance variations, but none have been found to be fully satisfactory.